dancing with design

radmix

I have a project with extruded plates at design will run at 130*. The same house has a slab in basement that will run at 110* at design. How much of a temp. difference would you allow before adding a second mix. would a 10 to 20* difference justify the extra cost of piping and controls

Jeremy_5

Seprate zone

If it's just the basement and ON IT'S OWN ZONE I would leave it all one temp. 130 is not above the max for concrete and basement slabs don't tend to run much anyway. The higher temp would also alow for any future use of the basement ie: a carpet. What tube spacing did you design with? You may also be able to spread them out to lower required temp.
Jeremy

Brad White

Yes

Even five degrees can make a sensible difference, how that water temperature translates into floor temperature hence output.

The key is, what is your final surface temperature, your floor covering and what is your heat loss in those spaces?

Also, what is the mass of the floors? If a low-mass floor, it may well tolerate valve/volume control whereas a dense slab will prefer constant circulation and delicate temperature changes at lower temperatures.

However, with this setup, your lower-mass floor (in the upper part of the house with higher heat loss) may well require higher temperatures if the conductivity is less than your high mass (in the basement with lower heat loss). You can see how different flavors (temperatures) corresponds to proper control.

Naturally your low mass floor with the higher temperature will govern and your slab will need to be mixed down from that. Master-Slave is a possibility giving the low mass priority. But you will need two temperatures, if I were designing it.

If you want to use the same temperature to a number of spaces with different emitter profiles and heat losses it raises the question, why zone at all?

EDIT: So long as you have the means to go back later and add a mix-down station, do what you like and see how it goes.

My $0.02

Brad

Constantin

What me, worry? :-P

... IIRC, my emitters upstairs also have a lower output than the slab in the basement (3/8" under wood vs. 1/2" in the slab). It just means that the basement zone runs a lot less than the circs upstairs. When it runs, the return temps are very low... but that's just me (homeowner, not pro).

I suppose you could install a proportional mixing valve that maintains a ΔT between the high-temp circuits for the upstairs areas and the slab in the basement. My understanding is that some of them can be proportional, i.e. create little offset at lower temperatures, and higher offsets at higher temperatures. This would be an important feature, otherwise your slab might be too cold in the shoulder seasons (with a fixed offset).

A FHV valve from Danfoss could also throttle the energy input into the slab quite effectively. If you have a constant-circulation design with TRVs for the rest of the house, this could be another KISS choice.

You could add another motorized mixing valve... but for a single circuit like the slab, I would consider something inexpensive, like an iSeries 3-way from Taco. It's a simple little device, several contractors here (like Jack Ragusa) have used it to good effect and it can include outdoor reset control.